Add extension methods in Angular 11 library

Question

Some time ago I created two simple file to extend functionalities for some types. I created a global.d.ts in this way:

export { }

declare global {
    interface Date {
        isLeapYear() : boolean;
    }

    interface Array<T> {
        contains(item: T, compareFunc?: (value: T) => boolean): boolean;
        sum(callbackfn: (value: T) => number) : number;
    }

    interface Element {
        closest(selector: string) : Element;
    }

    interface String {
        contains(text: string) : boolean;
    }
}

Then I created file extensions.ts whit implementations on the prototype. I imported it in my polyfills.ts:

import "zone.js/dist/zone";
import "./extensions";

In this way I'm able to use these methods everywhere in my code. Now I need to do the same thing in an Angular 11 library. I created global.d.ts and extensions.ts, but now? There isn't a polyfills.ts file and if I try with a simple import where I need one of this methods (import "../../extensions";) nothing works. In the console I obtain this errors:

projects/test_library/src/components/test.component/test.component.ts:428:48 - error TS2339: Property 'isLeapYear' does not exist on type 'Date'.

428                         return new Date(value).isLeapYear();
                                               ~~~~~~~~~~~~~~~~~
projects/test_library/extensions.ts:2:20 - error TS2339: Property 'isLeapYear' does not exist on type 'Date'.

2     Date.prototype.isLeapYear= function () : string {

How can I import globally my extensions? And why I get TS2339 error in extensions.ts when in other projects it works fine?

Tyrelltyrian

There is no possibility to add polyfills to an Angular Library, there is reasoning about it here: github.com/angular/angular-cli/issues/… Can it be an option, that the library declares and implements these methods and they will be imported in the polyfills.ts of the consumer application? – Apodictic